DC Power Sources 271

AC

Alternating current. Electricity that reverses direction at regularly recurring intervals of time. AC supplied by the U.S. electrical grid switches direction 120 times per second, or at 60 hertz (Hz).

alkaline battery

A primary cell battery that consists of a zinc anode, a manganese dioxide cathode, and an alkaline electrolyte. Alkaline batteries are small, lightweight, and durable.

alternating current

AC. Electricity that reverses direction at regularly recurring intervals of time. Alternating current supplied by the U.S. electrical grid switches direction 120 times per second, or at 60 hertz (Hz).

amperage

The amount of current flowing through a circuit. Amperage is measured in amperes (A), or amps.

anode

The negative electrode in a cell. The anode reacts with the cathode to release electrical energy.

arc welding

A joining process that uses heat generated by electricity to melt metals and form an airtight joint. Arc welding applications often use compound DC generators.

armature

The component of a generator in which current is induced. The armature usually consists of a series of coils or groups of conductors surrounding a core of iron.

armature windings

A conducting wire wrapped around the armature of a generator. Armature windings can connect in series, parallel, or both.

batteries

A device that uses metallic elements to convert chemical energy into electrical energy. Batteries produce direct current electricity.

bearings

A friction-reducing device that allows one moving part to glide past another moving part. Bearings help facilitate the rotation of the armature in a generator.

bidirectional

Moving in two different directions. Alternating current is bidirectional.

brushes

A sliding electrical contact that transfers current between the armature of a DC generator and the external circuit. Brushes contact segments of the commutator, which connect to different armature windings.

byproduct

A material created in addition to the primary product of a chemical reaction. Byproducts are sometimes harmful to the environment.

capacity

The amount of energy a power source can provide. The capacity of a battery depends on its materials and volume.

cathode

The positive electrode in a cell. The cathode reacts with the anode to release electrical energy.

cells

A single unit of a battery. A cell contains two different metals in an electrolyte solution.

charging cycle

The process of restoring the chemical reactivity of a secondary cell battery. The charging cycle involves forcing DC back through the battery.

circuit

A controlled path for electricity. A circuit includes a source, path, load, and control.

coil

A length of conducting wire in which a voltage is induced. Coils in an armature are wrapped around different axes to produce smoother output voltage.

commutator

The rotating device that transfers current from the armature of a DC generator to the brushes. The commutator maintains DC even though the polarity of the armature changes as it rotates.

compound generator

A DC generator that has field windings connected to the armature in both series and parallel. The compound generator combines the positive qualities of series and shunt generators.

conductor

A material that allows free movement of electrons and therefore allows easy flow of electricity. Conductors are typically metals.

conventional current theory

The belief that electricity flows out from a positive source to seek a negative conclusion. Conventional current theory has been replaced by electron theory but is still accepted by some fields.

copper loss

An electrical loss caused by the resistance of a conducting wire. Copper loss dissipates voltage into heat as current travels through a conductor.

corrodes

Experiences a deterioration in useful properties due to oxidation. Corroded metals can no longer react to produce voltage.

current

The flow of electricity. Current strength is called amperage and is measured in amperes (A).

DC

Direct current. Electricity that travels in one direction. DC does not reverse the direction of flow.

direct current

DC. Electricity that travels in one direction. Direct current does not reverse the direction of flow.

directly proportional

A relationship between two values in which one number increases or decreases at the same rate and ratio as another number. The amount of voltage produced by magnetic induction is directly proportional to the number of flux lines cut per second.

discharging cycle

The chemical reaction process of a battery that produces electricity. The discharging cycle is complete when a battery can no longer react to produce voltage.

distribution systems

A network of electrical components that provides electricity from the utility to specific end destinations. A distribution system uses generators, power lines, and transformers to deliver electric power to buildings and other structures.

doped

Enriched with trace amounts of other elements to increase electrical conductivity. Doped semiconductors are used in diodes and solar cells.

eddy currents

A swirling current induced in solid metals by changes in the magnetic environment. Eddy currents create heat that can lead to magnetic efficiency losses.

eddy-current loss

A magnetic loss caused by circulating eddy currents in a metal. Eddy-current loss occurs in generators because the changing polarity of the rotating armature induces eddy currents in the armature core.

efficiency

The ratio of a system or device’s output energy to the total energy supplied to it. Efficiency ensures that electrical systems do not waste large amounts of power.

efficiency losses

A decrease in output voltage caused by mechanical, electrical, and magnetic effects that occur naturally in a generator. Efficiency losses can be minimized, but no generator is 100% efficient.

electric vehicles

EVs. A vehicle that is fully or partially propelled by an electric motor that draws its power from a battery. Electric vehicles require high-energy rechargeable batteries.

electrodes

A device within a circuit that conducts electricity. Electrodes have a positive or negative charge.

electrolyte

A conductive solution containing an acid, an alkaline, or a salt. The electrolyte in a battery, fuel, or solar cell provides a connection between the two electrodes.

electromagnets

A magnet that gains an attractive force only when current passes through it. Electromagnets for generators are formed by connecting pole pieces and field windings.

electromotive series

A list of metals in order from most reactive, or most likely to give up electrons, to least reactive. The electromotive series is used to select metals for battery electrodes.

electron theory

The belief that electricity flows out from a negative source to seek a positive conclusion. Electron theory replaced conventional current theory and is currently accepted as correct.

electrons

A negatively charged particle that orbits the nucleus of an atom. Electrons flowing between atoms causes electricity.

energy storage systems

A device or group of devices capable of storing energy in order to supply electrical energy at a later time. Energy storage systems often use rechargeable batteries to store power.

EVs

Electric vehicles. A vehicle that is fully or partially propelled by an electric motor that draws its power from a battery. EVs require high-energy rechargeable batteries.

excitation current

Initial current supplied to a generator to energize the magnetic field. Excitation current is provided by an external DC power source.

exciter

A generator that allows another generator to become self-excited after an initial excitation current is provided. An exciter is mounted to the shaft of a DC generator’s armature.

field windings

A conducting wire that connects the pole pieces in a generator. Field windings energize the pole pieces to create electromagnets that form a magnetic field.

fossil fuels

Any naturally occurring organic fuel formed in the Earth's crust that can be burned to release stored energy. Fossil fuels include petroleum, coal, and natural gas.

friction

A force that resists the movement of two objects sliding against each other. Friction causes heat that can lead to mechanical efficiency losses.

frogleg-wound armature

An armature with windings connected in series-parallel. Frogleg-wound armatures are more common than lap- and wave-wound armatures.

fuel

A substance that undergoes a reaction to produce power. Fuel may take many forms, including liquid gasoline and hydrogen gas.

fuel cells

A device that converts chemical energy from gaseous or liquid fuels into electrical energy. Fuel cells are potentially very efficient power sources.

generators

A device that converts mechanical energy into electrical energy. Generators operate on the principle of magnetic induction.

green energy

A type of energy that is produced using methods or resources that cause no harm to the natural environment. Green energy sources include solar, wind, and water power, as well as hydrogen fuel cells.

hydrogen

H. A colorless, odorless gas that is the most abundant element on the planet. Hydrogen gas is converted into electrical energy in hydrogen fuel cells.

hydrogen fuel cell

A device that uses the chemical energy of hydrogen to produce electrical energy. A hydrogen fuel cell uses reverse electrolysis to produce electricity and releases heat and water as byproducts.

hysteresis loss

A magnetic loss caused by molecular friction in a conductive material. Hysteresis loss occurs in generators because the changing polarity of the rotating armature causes molecules to rub against each other.

laminations

A thin sheet of metal stacked and sealed with other sheets to form a conductive core. Laminations help reduce eddy-current loss.

lap-wound armature

An armature with windings connected in parallel. Lap-wound armatures are used for high-current, low-voltage loads.

left-hand flux rule

A method used to determine the direction of magnetic flux in relation to the direction of current flow in a conductor. The left-hand flux rule uses the thumb to show the direction of current flow and the fingers to show the direction of flux.

left-hand generator rule

A method used to determine the direction of current flow induced in a generator. The left-hand generator rule uses the index finger, thumb, and middle finger to show the direction of flux, conductor movement, and current flow, respectively.

lines of flux

An imaginary line of force that exits a magnet’s north pole and returns to its south pole or to the south pole of another magnet. Lines of flux form a magnetic field around a magnet.

lithium-ion battery

Li-ion battery. A secondary cell battery that uses a lithium compound as the cathode, a lithium salt electrolyte, and, usually, a graphite anode. Lithium-ion batteries are widely used in portable electronics and electric vehicles.

load

A component in a circuit that converts electrical energy into light, heat, or mechanical motion. Examples of loads are light bulbs, appliances, and machines.

magnetic field

The area in and around a magnet in which a magnetic force exists. Magnetic fields exhibit the powers of attraction and repulsion.

magnetic induction

The use of magnets to produce voltage in a conductor. Magnetic induction occurs whenever a conductor and magnetic lines of flux move in relation to one another.

negative

An electrical charge with a surplus of electrons. A negative charge is symbolized by a minus sign (-).

output voltages

The amount of electrical pressure or potential that is produced by a power source. The output voltage of a generator depends on the number of flux lines cut per second.

oxidize

To release or remove electrons from an atom, an ion, or a molecule. The anode of a battery oxidizes as it discharges.

oxygen

O. A colorless, odorless, tasteless gas that naturally exists in the atmosphere. Oxygen is used in hydrogen fuel cells to react with hydrogen and produce a voltage.

parallel

An electrical route that has multiple paths on which current can flow. Field windings connected in parallel with the armature consist of many turns of thin wires.

permeability

A material's tendency to become magnetized. Permeability can affect a material’s sensitivity to hysteresis loss.

photons

A particle of light energy produced by the sun. Photons are converted into electricity by solar cells.

photovoltaic cell

A device that uses semiconductors to convert light energy into electrical energy. Photovoltaic cells are also known as solar cells.

PN diode

An electrical semiconductor device that has one positively charged side and one negatively charged side. A PN diode allows current to flow only from the negative side to the positive side.

polarity

Having two oppositely charged poles, one positive and one negative. Polarity determines the direction in which current flows.

pole pieces

A device mounted on the inside of a generator that produces a magnetic field when energized. Pole pieces are connected to field windings to form electromagnets.

positive

An electrical charge with a shortage of electrons. A positive charge is symbolized by a plus sign (+).

power source

The device that provides electrical energy to a circuit. Power sources include batteries, generators, and other devices.

primary cell battery

A battery that cannot be recharged. Primary cell batteries are usually thrown away once their charge is spent.

reactive

Having a tendency to chemically react with other substances. Reactive metals are used as anodes in battery cells.

renewable energy

Energy that is naturally and continually replenished without being depleted. Renewable energy sources include sunlight and wind.

residual magnetism

The attractive force that exists in an object or substance after it has been removed from a magnetic field. Residual magnetism in the pole pieces energizes the field of a self-excited generator.

reverse electrolysis

An electrochemical reaction that occurs when hydrogen and oxygen combine. Reverse electrolysis produces electricity, heat, and water vapor.

secondary cell battery

A battery that can be recharged. Secondary cell batteries are charged by running current back through them to restore their chemical potential.

self-excited generator

A generator in which the field is energized by the residual magnetism of the pole pieces. Self-excited generators are portable but experience greater voltage drop than separately excited generators.

semiconductor

A material that restricts electrons but still allows them to flow. Semiconductors, such as silicon, have more electrical conductivity than insulators but less than conductors.

separately excited generator

A generator in which the field is energized by an external source of DC. Separately excited generators provide better voltage control and allow for a wider range of output voltages than self-excited generators.

series

An electrical route that has only one path on which current can flow. Field windings connected in series with the armature consist of a few turns of thick wire.

series generator

A DC generator that has field windings connected in series with the armature. The series generator is not very efficient.

series-parallel

A compound connection that uses both series and parallel routes. Series-parallel connections are used in frogleg-wound armatures.

short circuits

An electrical fault that occurs when current takes a shorter, unintended path between two conductors. Short circuits can be caused by damaged insulation, unintentional contact between conductors, or water coming into contact with circuits.

shunt

A winding designed to be connected in parallel with the armature of a DC motor or generator. Shunt fields consist of many turns of thin wire.

shunt generator

A DC generator that has field windings connected in parallel with the armature. The shunt generator is self-protected and provides high speed.

silicon

A lustrous, blue-gray, semimetallic crystalline material that is hard and brittle. Silicon is a semiconductor that is often used in devices like diodes.

solar cells

A device that uses semiconductors to convert light energy into electrical energy. Solar cells are also known as photovoltaic cells.

solar panel

A circuit of linked photovoltaic cells. Solar panels are used to provide large amounts of solar power.

stepped down

Transformed to a lower voltage. AC can be stepped down, but DC cannot be transformed effectively.

terminal

A connecting point in a circuit where a conductor can be attached to connect a component. Terminals are either negative or positive.

torque

A force that causes rotation. Torque determines how much work a motor or generator can accomplish.

transformed

Increased or decreased in voltage. AC can be transformed, but DC cannot.

turn

One loop or wrap of conducting wire in a coil. The number of turns in an armature coil affects generator output voltage.

unidirectional

Moving in only one direction. Direct current is unidirectional.

V

Volt. A unit of measurement that indicates the amount of electrical force or pressure in a circuit. The V unit measures voltage, which is also known as electromotive force.

volt

V. A unit of measurement that indicates the amount of electrical force or pressure in a circuit. The volts unit measures voltage, which is also known as electromotive force.

voltage

The amount of electrical pressure or potential that forces current to flow through a circuit. Voltage is measured in volts (V).

voltage drop

A decrease in voltage that occurs when current passes through resistance. Voltage drops occur as current travels along a conductor or through a load.

volume

The amount of three-dimensional space that an object occupies. Volume is measured in cubic feet or gallons in English units and in liters or cubic meters in metric units.

wave-wound armature

An armature with windings connected in series. Wave-wound armatures are used for high-voltage, low-current loads.

windage

A force that resists movement between air and a moving object. Windage causes heat that can lead to mechanical efficiency losses.